This invention relates generally to closed-circuit rebreathing apparatus using CO.sub.2 absorbers.
In general, commonly used absorbers incorporate solid, non-flexible containers to hold the absorbent materials, which are usually granulated pellets. Conventional rebreathing apparatus includes rigid cylindrical cartridges for the containment of the absorbent granules. The manufacturing, tooling and shipping costs of rigid containers are relatively high.
In addition, rigid containers allow little movement of the absorbent granules. Free movement of granules inhibits agglomeration and allows the presentation of new absorbent surfaces to the gas as the granules change position.
Yet another deficiency of rigid containers in rebreathing apparatus is that temperature differentials on the smooth metal or plastic inner surface of such rigid containers often result in condensation forming on those surfaces. To the extent that the condensation drips on, or otherwise contacts, the granules, the absorptive capabilities of such granules are greatly decreased. Conventional devices use various techniques to minimize this deficiency, such as multiple flexible outer bags surrounding the rigid container, heat shields to localize the condensation and sponges to soak up whatever condensation forms. Such conventional devices are described in the literature (see, for example, U.S. Pat. Nos. 4,502,876 and 4,764,346).
A further deficiency of rigid containers in rebreathing apparatus is that a number of low-resistance flow paths may develop through such containers. One effect of such "tunneling" or blow-through is that the absorptive capabilities of granules adjacent to the low-resistance flow paths diminish much earlier than those of granules located elsewhere. A second effect of blow-through is that a significant volume of gas bypasses the granules completely, such that no absorption of this gas takes place.